1. Field of the Invention
The invention relates to a ceramic bearing comprising a ceramic outer ring, a ceramic inner ring, and a ceramic sliding ring which is fitted between the ceramic outer ring and the ceramic inner ring.
2. Prior Art
A bearing such as a sliding bearing or a roller bearing is commonly used for housing a rotating shaft in an assembly. The roller bearings comprise rolling members such as balls, rollers, or needles, which are positioned between an outer ring fitted into a housing provided in a mechanical frame, and an inner ring into which the rotating shaft is installed. The roller bearings are classified as ball, roller, or needle bearings according to the type of rolling member used (Japanese Patent Publication No. 49-41231).
Among the roller bearings, deep-groove type, angular ball type, and tapered-roller type bearings are used for supporting a shaft to which radial and thrust loads are applied at the same time.
Some of the sliding bearings include a steel, cast iron, or copper support upon which a white metal layer is laminated and formed to a predetermined dimension by machining. Others of the sliding bearings include a copper or gun-metal support having an oil-impregnated alloy which is laminated upon or embedded into the support.
A sliding bearing having a sleeve-shaped support is known as a bearing for supporting radial loads (Japanese Patent Publication No. 49-18885). In addition, a sliding bearing having a metal support formed in disk-shape is known for supporting thrust loads (Japanese Patent Publication No. 49-678).
The roller and sliding bearings are standardized, being commonly available and having common features. In practice, these bearings are designed and selected according to the requirements of the application for which they will be used. However, the known sliding and roller bearings are deficient in some areas.
A number of problems may arise with the known roller bearings. Flaking of rolling members due to fatigue limits service life, and worn rolling members make the bearing noisy. The roller bearings have low heat resistance. Additionally, the roller bearings are costly due to a relatively larger number of components.
The known sliding bearings exhibit a different and distinct set of problems. Sliding friction between an outside circumference of a shaft journal and an inside circumference of the bearing generates heat. The amount of heat generated depends on the load applied to the shaft and the sliding speed. The amount of heat increases as the sliding speed and/or load increases. The heat causes thermal expansion of the shaft and the bearing, and is likely to adversely affect smooth rotation of the shaft. In addition, as the shaft journal and the inside circumference of the bearing slide in close contact with each other, wear results on the shaft and the bearing, and the wear also may obstruct the smooth rotation of the shaft.
Additionally, for sliding bearings, a load per unit area which the sliding bearing can support depends on the bearing material. In conventional sliding bearings, iron or copper-based metal is the material employed; however, the allowable load per unit area for the metals is smaller than that for ceramics. Therefore, a large bearing area is needed to support a large load, and the size of the sliding bearing becomes quite large. Further, for the sliding bearings, when supporting a shaft to which thrust and radial loads are applied at the same time, a sleeve-shaped radial bearing and a disk-shaped thrust bearing must be utilized in combination, or a bearing suitable for the application must be designed each time.